Just came upon this over on the Steam store listing's Updates section ... and there appears to be a newly added build at time of writing this message, I'm guessing that contains the latest updates (described below)

source: https://store.steampowered.com/news/app/1919470/view/3906372406946855027?l=english


"Happy Holidays Atarians!

A brand new batch of games for Atari 50 is here! Just in time for the Holidays, download this free content update including a dozen Atari classics and homebrews. Boot up Double Dunk, Warbirds, Return to Haunted House, and more on the first content update for Atari 50.

Check out the full patch notes below for the full list of titles added!

Patch Notes:

Added the following games:

Adventure II (homebrew) 2600
Bowling 2600
Double Dunk 2600
Maze Craze 2600
Miniature Golf 2600
MotoRodeo 2600
Aquaventure (prototype) 2600
Save Mary (prototype) 2600
Super Football 2600
Return to Haunted House (homebrew) 2600
Circus Atari 2600
Warbirds Lynx

Minor bug fixes"

Does the GOG version include this Holiday Content Update?

The game is updated to the latest version here, on GOG, including those games and the reimagination of haunted house and so.